The present invention relates generally to data storage devices. More specifically, the present invention relates to a method and storage media configuration that provides for the reliable identification of data storage sectors on the storage media.
As is well known in the data storage field, data storage media is typically configured to have a plurality of sectors identified on the surface thereof, with each sector being identified by a specific address. Each sector typically has a preformatted header, which is utilized for addressing and synchronization purposes. These headers are typically preformatted and often include information (i.e., embossed data) coded in a manner that is similar to the recorded data on the media. Since the header information is coded in this manner, reading of this information is obviously done in the same manner that the actual data is read. More specifically, this typically requires first locking a PLL to the header preamble (i.e., VFO) in order to obtain appropriate synchronization. Once this synchronization is achieved, an address mark is typically detected, followed by address data, which once again is coded in a manner similar to the recorded data on the media (e.g., run length limited encoded data like 1,7 RLL code or 2,7 RLL code).
As will be appreciated, the utilization of a header with identification data stored in this format requires the use of several cooperating systems. As mentioned above, a phase-locked loop (PLL) is required in order to provide synchronization with the header. Additionally, the decoding of address data requires the use of slice levels and gain control loops to insure the information is appropriately deciphered. While each of these systems can be implemented, they are also prone to inherent errors. For example, the inaccurate maintenance of slice levels, due to defects or mark-space asymmetry, can easily result in data errors. Additionally, inaccurate PLL capture can obviously skew timing, also creating errors in reading header data. Those issues can be dealt with when reading recorded data from a storage media because the recorded data is typically protected by an Error Correction Code (ECC) and additional re-synchronization fields. Applying those same techniques to the headers would significantly increase their overhead and thus would reduce the space available for data recording. Adding ECC to the Headers would also make the drive electronics more complex. Hence headers typically only contain a simple Error-Detection method such as a Cyclic Redundancy Check (CRC).
In addition to the complexities discussed above, the typical present day header requires a very large preamble, thus limiting the amount of information which can be stored. For example, with a large preamble it is not possible to repeat the address information multiple times as there is simply not a reasonable amount of space within the designated header area. Consequently, it would be beneficial to reduce the amount of “header overhead,” thus allowing additional space for more critical information, such as address information.
Referring to FIG. 1, there is shown one example of a classical header which utilizes the above-mentioned synchronization and addressing scheme. Referring specifically to FIG. 1, this classical header or RLL coded header 10 begins with a sector mark 12 which identifies the beginning of the new section. Following sector mark 12, a synchronization field 14 is utilized to allow the phase locked loop to synchronize with this section on the media. Following synchronization, an address field 16 provides a first address (ID1) for the particular section. A second synchronization field 18 is then encountered followed by a second address field 20 (ID2). Utilizing two synchronization fields and two address fields provides some redundancy in the addressing scheme.
As shown in FIG. 1, this first sequence of fields is written to the land section of the media. Next, a Quadrature Wobble Mark field 22 is encountered, which provides information about track alignment. The readout then jumps to the groove section 32 of the media. These same fields are then repeated in a checkerboard fashion. As illustrated in FIG. 1, the synchronization fields utilize a large amount of space on the media. Once again, this highlights the amount of overhead required for this synchronized header addressing methodology.
In addition to the issues related to overhead, the sector mark 12 used in this traditional header is potentially problematic. Sector mark 12 could be obscured by dust particles, making them undetectable. Should this happen, the entire sector becomes unreadable and additional operations must be initiated (e.g., relocate the sector, etc.). This same problem also arises when media defects exist.
As mentioned above, the header information is often times preformatted on the disk during the manufacturing operations. As can be appreciated, this pre-formatting must be accomplished utilizing fairly tight tolerances and specifications for the pre-formatted pits. This obviously adds to the complexity and cost of the media itself. Consequently, any effort to simplify things is very beneficial.
In addition to the above-referenced challenges, storage media itself is getting more and more complex. To increase data capacity, the density of data on the storage media is being increased using smaller and smaller marks and spaces on the media surface. In order to deal with this increase in density in optical storage systems, thinner dust defocusing cover layers are being utilized, and the optical pick-up needs to operate much closer to the media itself. While this is very effective to increase the density of the storage media, it has a detrimental effect on the media's ability to deal with contamination and dust. As can be imagined, a dust particle on the media surface will distort the readout, making the reading of data inaccurate. This distortion affects a larger region of the media when the optical pick-up is closer to the surface. The same is true for holes in the reflective layer and data replication defects. When dust or defects are encountered in a header, the address data becomes unreliable and cannot be used. Consequently, the data-sector following this address data cannot be used. This creates the need for adjustments to be made in the data storage system, such as relocation to other areas. Redundancy in the address data is one solution for this problem, but is limited by space constraints within the header. That is, the size of the header only allows address data to be repeated a limited number of times.
Furthermore, these higher densities also make it more difficult to deal with manufacturing imperfections and defects in the media itself. These defects typically affect areas on the media—sometimes large areas. The above-referenced header formats complicate the problem of those defects by containing large amounts of non-redundant information in relatively concentrated areas on the disk.
In light of the issues raised above, it would be beneficial to design a header format which is robust and reliable. This desired format would easily deal with dust and media defects, and provide an efficient use of header space. Further, the preferred header format would anticipate the issues raised by increased data density, and attempt to simplify the process of reading header information.